2.1 Breast cancer is the most common type of cancer among women in the UK. Women have a one in nine lifetime risk of developing breast cancer. The incidence of breast cancer increases with age, doubling every 10 years until menopause, after which the rate of increase slows down. In the UK, 45,972 people were diagnosed with breast cancer in 2007, of whom over 99% were women.
2.2 Metastatic breast cancer is an advanced stage of the disease when it has spread to other organs. An estimated 5% of patients present with metastatic breast cancer, and approximately 30% of people who present with localised breast cancer will later develop metastatic breast cancer. Common sites of metastasis include bone, liver, lung and brain.
2.3 When clinicians manage breast cancer they consider various prognostic factors, including hormone receptor status and HER2 status. Hormone receptors include oestrogen receptors and progesterone receptors. Tumours that express either oestrogen receptors or progesterone receptors are commonly referred to as being hormone receptor positive. It is estimated that 60% and 80% of all breast cancers in premenopausal and postmenopausal women respectively are hormone receptor positive. People with hormone-receptor-positive breast cancer generally have a better prognosis than those with hormone-receptor-negative breast cancer.
2.4 Tumours that overexpress the HER2 protein (HER2+) grow and divide more quickly, so women with HER2+ tumours generally have a worse prognosis than women with HER2 negative tumours. Approximately 20–30% of people with metastatic breast cancer have HER2+ tumours, of which about 50% will also be hormone receptor positive. In this appraisal, estimates from consultees and clinical specialists for the number of women per year with newly diagnosed metastatic breast cancer who have tumours that are HER2+ and hormone receptor positive ranged from 50 to 2000.
2.5 The aim of treatment in metastatic breast cancer is to palliate symptoms, prolong survival and maintain a good quality of life with minimal adverse events. Choice of treatment depends on previous therapy, hormone receptor status, HER2 status and the extent of the disease. 'Advanced breast cancer: diagnosis and treatment' (NICE clinical guideline 81) recommends that if the disease is not imminently life threatening, or does not need early relief of symptoms because of significant visceral organ involvement, women who are postmenopausal and have hormone-receptor-positive breast cancer should be offered an aromatase inhibitor such as anastrozole or letrozole. There is variation in clinical practice for people with tumours that are both HER2+ and hormone receptor positive.